This invention is generally directed to photoresponsive imaging devices, and more specifically the present invention is directed to improved layered photoresponsive or photoconductive imaging devices containing a substrate, a photogenerating layer, a charge transport layer, and a ground strip hole injecting electrode in contact with a portion of the hole transport layer. In one embodiment of the present invention, a strip of the hole injecting electrode which is attached to the non-image areas of the hole transport layer is comprised of a mixture of conductive particles, such as carbon black, dispersed in a resinous binder material. The improved photoresponsive devices of the present invention are useful as imaging members in electrostatographic imaging systems, particularly xerographic imaging systems, wherein latent images are formed thereon, and made visible by developer compositions containing toner particles and carrier particles. When used in such systems, the improved photoresponsive devices of the present invention are generally charged negatively.
Electrostatographic imaging systems, which are well known involve the formation and development of electrostatic latent images on the surface of photoconductive materials referred to in the art as photoreceptors or photosensitive compositions. In these imaging systems, and in particular in xerography, the xerographic plate containing the photoconductive insulating layer is imaged by uniformly electrostatically charging its surface, followed by exposing the layer to a pattern of activating electromagnetic radiation such as light, which selectively dissipates the charge in the illuminated areas of the photoconductive member causing a latent electrostatic image to be formed in the non-illuminated areas. This latent electrostatic image can then be rendered visible with developer compositions containing toner particles and carrier particles. Many known photoconductive members can be selected for incorporation into the electrostatic imaging system including, for example, photoconductive insulating materials deposited on conductive substrates, as well as those containing a thin barrier layer film of aluminum oxide situated between the substrate and the photoconductive composition, primarily for the purpose of preventing charge injection from the substrate into the photoconductive layer upon charging of its surface, as charge injection could adversely affect the electrical properties of the photoreceptor, and thus the quality of the resulting images.
Examples of photoconductive members include materials comprised of inorganic materials and organic materials, layered devices comprised of inorganic or organic materials, composite layered devices containing photoconductive substances dispersed in other materials, and the like. An example of an early type of composite photoconductive layer used in xerography is described, for example, in U.S. Pat. No. 3,121,006 wherein there is disclosed a number of layers comprising finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resinous binder. Examples of specific binders disclosed in this patent include, for example, polystyrene resins, silicone resins, acrylic and methacrylic ester polymers, polymerized derivatives of acrylic and alpha acrylic acids, chlorinated rubbers, vinyl polymers, and co-polymers, and cellulose esters.
Illustrative examples of other known photoconductive compositions include amorphous selenium, halogen doped amorphous selenium substances, amorphous selenium alloys, including selenium arsenic, selenium tellurium, selenium arsenic antomony, halogen doped selenium alloys, wherein the halogen is a material such as chlorine, fluorine, or bromine, such halogen generally being present in amounts of 50 parts per million to about 1,000 parts per million, cadmium sulfide, and the like. Generally, these photoconductive materials are deposited on suitable conductive substrates, and incorporated into the xerographic imaging system for use as the imaging member.
Recently, there has been disclosed negatively charged layered photoresponsive devices comprised of photogenerating layers and transport layers deposited on conductive substrates, reference, for example, U.S. Pat. No. 4,265,990, and overcoated photoresponsive materials containing a hole injecting layer, overcoated with a hole transport layer, followed by an overcoating of a photogenerating layer, and a top coating of an insulating organic resin, as described, for example, in U.S. Pat. No. 4,251,612. Examples of photogenerating layers disclosed in these patents include trigonal selenium and various phthalocyanines; and as transport layers, there is described the use of certain diamines dispersed in inactive polycarbonate resinous binders. The disclosures of each of these patents, namely, U.S. Pat. Nos. 4,265,990, and 4,251,612 are totally incorporated herein by reference.
Additionally, there is disclosed in U.S. Pat. No. 3,639,121 an electrophotographic imaging element which is externally grounded during charging, and is comprised of a support layer, an electrically conductive layer overlaying the support, a photoconductive layer overlaying the conductive layer, and a layer of conducting lacquer distinct from the conductive layer coated on the edge of the element so as to electrically connect the conducting layer to external ground during charging of the element, the lacquer in one embodiment comprising a dispersion of conductive material, such as carbon black, or graphite, in a resinous binder polymeric binder, reference, for example, the disclosure in Col. 2, beginning at around line 26.
While the above-described photoresponsive devices are suitable for their intended purposes, there continues to be a need for improved devices. Additionally, there is a need for improved photoresponsive devices containing a hole injecting grounding electrode, which is not in contact with the conductive supporting substrate, allowing for the production of photoresponsive devices having consistent reliable properties with extended usage. Additionally, there continues to be a need for improved photoresponsive devices wherein precision coating processes are not needed for applying the grounding strip, and furthermore, the improved photoresponsive devices of the present invention can be prepared by simultaneously coating the grounding strip and charge transport layer.